The present invention relates generally to voice frame network systems such as Voice over Internet Protocol (VoIP) systems for concurrently carrying both voice and data signals, and more particularly it concerns method and apparatus for suppressing disruptive V.8bis negotiations during the startup phase of modem relay communication between two gateways. V.8bis herein refers generally to the historic and continually evolving ITU-T Recommendation V.8bis (standard) adopted by the International Telecommunication Union, familiarity with which is assumed.
Immediately below are a few definitions related to V.8bis:
V.8bis Signal: V.8bis information sent via tones.
Initiating Signal: A V.8bis signal, which initiates a V.8bis transaction.
Responding Signal: A V.8bis signal that is sent in response to an initiating signal.
V.8bis Message: V.8bis framed information sent at 300 bits/sec using V.21 channels.
V.8bis Transaction: A sequence of V.8bis signals and messages, beginning an initiating signal and terminating with either a positive acknowledgement, a negative acknowledgement or a timeout.
Answering Station: Client device that answers a PSTN call.
Calling Station: Client device which originates a PSTN call.
Initiating Station: Client device which initiates a V.8bis transaction, may be either the Answering or Calling Station.
Responding Station: Client device that responds to the initiator of a V.8bis transaction.
V.8bis-capable modems can exchange V.8bis transactions during call establishment phase or subsequently at later points during the “voice mode” (before transitioning the channel into “modem relay” mode).
The V.8bis capability is optional and only some modems presently support it. V.8bis transactions use signals or messages that are transmitted with adequate fidelity across a wide range of voice codes.
If both client devices are V.8bis capable, the V.8bis transactions would proceed during the voice mode (prior to Answer tone). These transactions result in complications and potential disruption. For example, the transactions might:                a) Modify subsequent V8 procedures. For example, shorten the V8 startup by eliminating V8 CM. Eliminating CM is detrimental, since it is a trigger into modem relay mode, and having it eliminated can fail successful transactions into modem relay mode.        
Additionally:                b) Some high speed proprietary modulations (prior to V.90) use V.8bis negotiations. This means V.8bis negotiations might result in client devices configuring themselves for a proprietary high-speed modulation, which may not be supported on most modem relay gateways. In the latter case, there would be call failure.        
As noted above, the V.8bis procedures are optional and occur only when both client devices are capable. Hence, these procedures are not required to achieve successful modem calls (since there is no guarantee both devices are capable). However, they can have a number of detrimental effects on mode relay operation, significantly complicating modem relay gateway implementation.